Occupational studies are conducted to identify and quantify chemical and other causes of cancer and to understand mechanisms of carcinogenesis. Major etiologic investigations focus on working populations exposed to benzene, other organic solvents, aromatic amines, acrylonitrile, formaldehyde, diesel exhausts, combustion products, and silica. Etiologic investigations utilize sophisticated industrial hygiene methods to assess occupational exposures and biochemical components to elucidate mechanisms of carcinogenic action and individual susceptibility. Findings during the past year include excesses of multiple myeloma and non-Hodgkin's lymphoma among aircraft maintenance workers exposed to solvents, particularly among women; elevated risks of leukemia, non-Hodgkin's lymphoma, and myelodysplasias among workers in China exposed to benzene; and a small, but intriguing, excess of lung cancer among workers heavily exposed to acrylonitrile. Major new efforts currently underway focus on workers exposed to benzene, miners exposed to diesel exhausts, fire fighters exposed to combustion products, and case-control studies of non-Hodgkin's lymphoma and cancers of the brain, stomach, lung, bladder, and breast to evaluate risks from exposure to solvents and other chemicals. Extended mortality follow-up is underway for previously completed cohort studies of workers exposed to formaldehyde, perchloroethylene, and other organic solvents. A survey of occupation and cancer mortality in 24 States provided a number of new clues about occupational cancer risks. Cytogenetic effects of formaldehyde and occupational causes of nasal cancer were investigated.